If you check the specs between the WRX and the ST. The WRX is only 817 lbs heavier. And the WRX is certainly no slouch when it comes to handling,and performance.
Now I am not bashing the ST and promoting the WRX. I am just looking at from the eye of a consumer who would be looking at cars in this class.

817lb difference is WAY off. WRX is actually relatively light considering it's AWD. There's only about a 50lb difference in curb weight between an ST and WRX.